Method and apparatus for transmitting SRS in LTE TDD system

ABSTRACT

A method and apparatus are provided for transmitting an uplink Sounding Reference Signal (SRS) by a User Equipment (UE). The method includes receiving information related to an SRS period and an offset for an SRS transmission; generating the uplink SRS; and when the information indicates the SRS period is 2 ms, transmitting the SRS in two Single Carrier Frequency Division Multiple Access (SCFDMA) symbols in a half frame according to the offset for the SRS transmission. When the information indicates the SRS period is 2 ms and a length of an Uplink Pilot Time Slot (UpPTS) in the half frame is two symbols, a first symbol in the UpPTS is indicated by offset 0 and a second symbol in the UpPTS is indicated by offset 1.

PRIORITY

This application is a Continuation Application of U.S. application Ser.No. 12/865,334, which was filed in the U.S. Patent and Trademark Officeon Jul. 29, 2010, now U.S. Pat. No. 8,520,492 and claims priority toInternational Appl. No.: PCT/KR2009/000050, which was filed on Jan. 7,2009, and to Chinese Patent Application No. 200810004863.0, which wasfiled on Feb. 5, 2008, the content of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system, especially to amethod for transmitting SRS in an LTE communication system and anapparatus using the same.

2. Description of the Related Art

3GPP (The 3rd Generation Partner Project) standardization organizationis working out a next generation of wireless communication standardwhich is named LTE (Long Term Evolution). In a physical layer interface,the new standard adopts OFDM (Orthogonal Frequency DivisionMultiplexing) technology, which is different from conventional CDMA(Code Division Multiple Access) technology. OFDMA is used in downlinkand SCFDMA (Single Carrier Frequency Division Multiple Access) is usedin uplink. The technology used in the new standard is effective toresist multi-path propagation, with the adoption of frequency domainequalization reducing complexity of the conventional time domainequalization, and is more suitable to bandwidth high-speed datatransmission.

From a point of view of air-interface, the LTE standard techniques canbe divided into two categories: a TDD (Time Division Duplex) system andan FDD (Frequency Division Duplex) system. The LTE system supportsvariable bandwidths. And typical bandwidths include 1.4 MHz, 3 MHz, 5MHz, 10 MHz, 15 MHz and 20 MHz, which can meet demands of differentscenarios.

FIG. 1 illustrates a physical layer frame structure for a LTE FDD systemin which a length of radio frame (101) is 10 ms, consisting of tenequally sized radio sub-frames (102) of 1 ms length. Each radiosub-frame consists of two equally sized timeslots (103) of 0.5 mslength.

FIG. 2 illustrates a PHY layer frame structure for LTE TDD system. Asshown in FIG. 2, a length of radio frame (201) is 10 ms, consisting often equally sized radio sub-frames (204) of length 1 ms. Each fivecontinuous radio sub-frames consists a half-frame (202) of length 5 ms.Different from the LTE-FDD system, a second (211) and seventh (212)radio sub-frame in LTE-TDD radio frame are two special sub-frames. Alength of the special sub-frame is 1 ms, consisting of three specialslots, indicating DwPTS (205 or 208), GP (206 or 209) and UpPTS (207 or210) respectively. The lengths of the three special slots are variableand are defined by system, and the total length is 1 ms. The length ofUpPTS can be 0, 1 or 2 SCFDMA symbols. If the length of UpPTS is 2,UpPTS is used to transmit the uplink Short RACH or Uplink SRS signal orboth the Short RACH and SRS signal. If the length of UpPTS is 1, UpPTSis used to transmit the uplink SRS signal. The other eight sub-framesexcept the special two are respectively consist of two slots (203) oflength 0.5 ms.

In the LTE system, according to network scheduling, UE (User Equipment)sends an SRS (Sounding Reference Signal) to eNodeB (evolved NodeB). TheSRS signal is used to: according to an analysis result of the SRSsignal, eNodeB estimates a quality of channel which is used fortransmitting SRS from UE to eNodeB and scheduling data according tofrequency selective characteristics; eNodeB performs timing tracking forUE by analyzing the SRS signal and performs a close-loop power control.According to a current standardizing process, main conclusions for SRStransmission in LTE FDD system include: eNodeB broadcasts the SRS in adesignated cell as needed and SRS is transmitted in some sub-frame in adesignated cell periodically. A period is selected from {2, 5, 10, 20,40, 80, 160, 320} ms. After UE receives the SRS in the designated cell,the ODFM symbol resource occupied by the SRS is not used whentransmitting uplink data. In order to perform the transmission of SRS,UE should receive a user-designated SRS signal transmitted from thenetwork. The signal informs the user of the OFDM symbol resource used totransmit SRS. Currently, there is no description for transmitting theSRS of designated UE in a PHY layer specification which is accomplishedin LTE.

Nowadays, a basic idea in the standard for the user-designated SRSsignaling is that the signaling includes three parts: Duration, Periodand Offset in which, the duration can use 1 bit to indicate that justone snapshot or infinite. The period value is selected from {2, 5, 10,20, 40, 80, 160, 320} ms. In LTE FDD, the offset is a time between twicetransmission time of each OFDM symbol of SRS from the beginning of theSRS period, and the basic unit is 1 ms. In LTE TDD, definition of offsetis different from that in LTE FDD. Since in LTE TDD, SRS can betransmitted in UpPTS or the other uplink sub-frame, the uplink sub-framemay be discontinuous and UpPTS occupy two OFDM symbols at most, theoffset is defined as an interval between an OFDM symbol position used totransmit SRS and an OFDM symbol position used to transmit SRS until theperiod of SRS transmission starts. For example, if the SRS symbolposition at the period beginning is defined as 0, a symbol position usedto transmit SRS is 3 means that the interval between the two symbols is3, there is at most 2 OFDM symbol positions can be used to transmit SRS.

The manner of transmitting SRS in LTE TDD is mainly the same as that inLTE FDD. However the system structure of LTE TDD is different from ofthat in LTE FDD. Difference is that in LTE TDD, a half-frame of length 5ms has both uplink sub-frame and downlink sub-frame, a number of uplinksub-frames and downlink sub-frames is configured by the network. In someconfiguration, a half-frame of length 5 ms at least has one uplinksub-frame (exclude UpPTS). According to a principle that only one SRS istransmitted in one uplink sub-frame, there is only one SRS transmissionin every 5 ms, and the system can't achieve the SRS transmission with a2 ms period. Therefore, the performance of SRS transmission by UE isdeteriorated in a fast Time-varying channel.

Based on the difference between the LTE TDD and LTE FDD, the currentconfiguration of the 2 ms transmission period for SRS in the LTE FDDcannot be used in the LTE TDD system.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to address at least theproblems and/or disadvantages described above and to provide at leastthe advantages described below.

An aspect of the invention is to provide a method for transmitting a SRSin an LTE TDD communication system. A format of SRS in LTE FDD and LTETDD will be the same.

In accordance with an aspect of present invention, a method is providedfor transmitting an uplink Sounding Reference Signal (SRS) by a UserEquipment (UE). The method includes receiving information related to anSRS period and an offset for an SRS transmission; generating the uplinkSRS; and when the information indicates the SRS period is 2 ms,transmitting the SRS in two Single Carrier Frequency Division MultipleAccess (SCFDMA) symbols in a half frame according to the offset for theSRS transmission. When the information indicates the SRS period is 2 msand a length of an Uplink Pilot Time Slot (UpPTS) in the half frame istwo symbols, a first symbol in the UpPTS is indicated by offset 0 and asecond symbol in the UpPTS is indicated by offset 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a frame structure in an LTEFDD system;

FIG. 2 is a schematic diagram illustrating a frame structure in an LTETDD system;

FIG. 3 is a schematic diagram illustrating the SRS transmission processof designated user in an LTE system;

FIG. 4 is a schematic diagram illustrating an SRS transmission processof LTE UE;

FIG. 5 is a schematic diagram illustrating seven types of uplink anddownlink configuration in an LTE TDD system;

FIG. 6 illustrates an example 1 according to present invention; and

FIG. 7 illustrates an example 2 according to present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

For the LTE FDD system, since the maximum period of SRS is among {2, 5,10, 20, 40, 80, 160, 320} ms, in order to achieve a maximum flexibility,for an arbitrary period, a possible SRS offset is select from {0, 1, . .. , Period−1}. Therefore, for the LTE FDD, the SRS of the designateduser includes 2+5+10+20+40+80+160+320=637 indexes. This method providesa maximum flexibility, and needs 10 bits to present 637 indexes. Since1024 pieces of information may be indicated by 10 bits, the other1024−637=387 indexes are reserved for various purpose.

When the period is 320 ms, providing at most 320 offsets is unnecessary,the 10 bits may be not the most reasonable. In this condition, thenumber of indexes can decrease with the decrease of the offset range, sothat a total number of bits needed decreases and the number of reservedindexes decreases.

UE receives an index N indicating a period of SRS transmission from basestation.

For a LTE TDD system, the period value of SRS is also among (2, 5, 10,20, 40, 80, 160, 320} ms, the design of offset is the same as in LTE FDDexcept that when the period is 2 ms and 5 ms. However compared with LTEFDD the difference is that in LTE TDD, the uplink sub-frame isn't alwayscontinuous, so that there doesn't have a complete period of 2 ms. Forthis reason, the period of 2 ms for LTE should have some special design.Currently, there are seven uplink and downlink configurations supportedin LTE TDD, illustrated in FIG. 5(501-507). A group of corresponding SRSindexes is defined to indicate the SRS index of designated user of 2 msperiod. For configuration of 0(501), 1(502), 2(503) and 6(507), all ofthe indexes indicate that in a 5 ms half-frame period or 5 ms frameperiod, two continuous or arbitrary OFDM positions in logical from theOFDM symbols which are configured to transmit SRS are selected, and thedesignated user is indicated to use this position to transmit SRS. Forconfiguration of 3(504), 4(505) and 5(506), all of the indexes indicatethat in a 10 ms frame period, two continuous or arbitrary OFDM positionsin logical from the OFDM symbols which are configured to transmit SRSare selected, and the designated user is indicated to use this positionto transmit SRS. The definition mentioned is used to inform thedesignated user that how to select the OFDM position used for SRStransmission in the 2 ms period.

Considering that in LTE TDD system, there are at most 5 OFDM symbolsused to transmit SRS in 5 ms half-frame, which include two symbols inUpPTS, and three OFDM symbols in uplink sub-frame 2, 3 and 4. Thus, ifthe two selected symbols are arbitrary, the number of choice isC(5,2)=10 (C presents for combination) with 10 corresponding indexes.Ten indexes need to correspond with the concrete OFDM symbols. Anycorrespondence will be used without departing from the spirit and scopeof the present invention. For example the correspondence may be selectedrandomly, or when making correspondence, assigning the indexes with highpriority to a former or latter position. One consideration aboutpriority is considering a situation with 1 or 2 UpPTS symbol first.There are four situations (a last OFDM symbol and a first OFDM symbolisn't logically continuous) or five situations (a last OFDM symbol and afirst OFDM symbol is logically continuous) if select two continuous OFDMsymbols, so that four or five indexes are needed for indicating.

If the period is 5 ms, a special case in LTE TDD is that, forconfiguration 3(504), 4(505) and 5(506), there is no uplink resource inthe second half-frame in 10 ms frame. So that SRS can't be transmittedin the second half-frame. If the two continuous or arbitrary OFDMpositions in logical are selected from the OFDM symbols configured totransmit SRS in the first half-frame, the definition is the same as inLTE TDD with 2 ms period. Therefore, in order to simplify the systemdesign, 5 ms period isn't suitable for configuration 3, 4 and 5 in LTETDD in present invention.

Compared with LTE FDD, in some situation, period of 2 ms and 5 ms aren'tsupported, so that the period of 2 ms and 5 ms is redefined to achieve asimilar function as in LTE FDD.

Based on the redefined method to redefine the 2 ms period ofconfiguration 0 to 2 and 6, an actual period is 5 ms, that is, two SRSsymbols are occupied every 5 ms. In order to redefine the 2 ms period ofconfiguration 3 to 5, the actual period is 10 ms, that is, two SRSsymbols are occupied every 10 ms. In fact, the redefinition describedabove for 2 ms and 5 ms period for LTE TDD can be used in systemconfiguration and makes the comparison with LTE FDD easy. Sometimes, thesystem doesn't support the period of 2 ms and 5 ms, and directly defineto configure two SRS in 5 ms or 10 ms. The essence of these two methodsis the same. The essence of the method is the same as the redefinitionof period. More specifically for the second method, SRS period of 2 msisn't supported in LTE TDD. For configuration 3 to 5, SRS period of 5 msisn't supported. However, two SRS symbols can be configured everyhalf-frame (every 5 ms), such as for configuration 0 to 2 and 6. Also,two SRS symbols can be configured in the first half-frame (every 10 ms)in radio frame, such as for configuration 3 to 5. The configuration oftwo SRS symbols in every half-frame can use a similar method comparedwith the method used in the redefinition of 2 ms and 5 ms perioddescribed above, so to speak, a completely flexible configuration needsto indicate C(5,2)=10 choices, or decrease the number of selection byrestrict the method of configuration, the invention is not limited.

Furthermore, the redefinition of 2 ms period described above is toconfigure two SRS symbols in a half-frame (5 ms), that is, it isreasonable to define that 2 ms period isn't support in LTE TDD systemand two SRS symbols is configured every half-frame (5 ms). Forconfiguration 0 to 2 and 6, the actual period is 5 ms, that's to saythat, two SRS symbols are occupied every 5 ms. For configuration 3 to 5,the actual period is 10 ms, that's to say that, two SRS symbols areoccupied every 10 ms. The configuration of two SRS symbols in everyhalf-frame can use a similar method compared with the method used in theredefinition of 2 ms and 5 ms period described above, that is, aflexible configuration needs to indicate C(5,2)=10 choices, or decreasethe number of selection by limiting the method of configuration, theinvention is not limited.

After the UE receives information N indicating SRS transmission from thenetwork, when the SRS period indicated by N is less than or equal to thenumber of OFDM symbols configured to transmit SRS in the entire cell ina period, the offset can be calculated as follows:

If the range of N is from 0 to 320/f−1, the period indicated by N is 320ms, then the SRS is transmitted by using offset N*f.

If the range of N is from 320/f to 320/f+160/m−1, the period indicatedby N is 160 ms, then the SRS is transmitted by using offset N−320/f*m.

If the range of N is from 320/f+160/m to 320/f+160/m+80/t−1, the periodindicated by N is 80 ms, then the SRS is transmitted by using offsetN−320/f−160/m*t.

If the range of N is from 320/f+160/m+80/t to 320/f+160/m+80/t+40/n−1,the period indicated by N is 40 ms, then the SRS is transmitted by usingoffset N−320/f−160/m−80/t*n.

If the range of N is from 320/f+160/m+80/t+40/n to320/f+160/m+80/t+40/n+20/p−1, the period indicated by N is 20 ms, thenthe SRS is transmitted by using offset N−320/f−160/m−80/t−40/n*p.

If the range of N is from 320/f+160/m+80/t+40/n+20/p to320/f+160/m+80/t+40/n+20/p+10/x−1, the period indicated by N is 10 ms,then the SRS is transmitted by using offsetN−320/f−160/m−80/t−40/n−20/p*x.

If the range of N is from 320/f+160/m+80/t+40/n+20/p+10/x to320/f+160/m+80/t+40/n+20/p+10/x+5−1, the period indicated by N is 10 ms,then the SRS is transmitted by using offsetN−320/f−160/m−80/t−40/n−20/p−10/x.

Where f, m, t, n can be 1, 2, 4, 8; p can be 1, 2, 4, 5, 10; x can be 1,2, 5; M presents a number of OFDM symbol configured to transmit SRS in aperiod in the whole cell indicated by information N. The value of f, m,t, n and M need to be set statically in system specification. “−” is asymbol for subtraction.

After UE receives the information N indicating the SRS transmission fromnetwork, when the SRS period indicated by N is greater than the numberof OFDM symbols configured to transmit SRS in the entire cell in aperiod, the offset can be calculated as follows:

If the range of N is from 0 to M−1, the period indicated by N is 320 ms,then the SRS is transmitted by using offset N;

Reserved by the system if the range of N is from M to 320/f−1;

If the range of N is from 320/f to 320/f+M−1, the period indicated by Nis 160 ms, then the SRS is transmitted by using offset N−320/f;

Reserved by the system if the range of N is from M to 320/f+160/m−1;

If the range of N is from 320/f+160/m to M−1, the period indicated by Nis 80 ms, then the SRS is transmitted by using offset N−320/f−160/m;

Reserved by the system if the range of N is from M to320/f+160/m+80/t−1;

If the range of N is from 320/f+160/m+80/t to M−1, the period indicatedby N is 40 ms, then the SRS is transmitted by using offsetN−320/f−160/m−80/t;

Reserved by the system if the range of N is from M to320/f+160/m+80/t+40/n−1;

If the range of N is from 320/f+160/m+80/t+40/n to M−1, the periodindicated by N is 20 ms, then the SRS is transmitted by using offsetN−320/f−160/m−80/t−40/n;

Reserved by the system if the range of N is from M to320/f+160/m+80/t+40/n+20/p−1;

If the range of N is from 320/f+160/m+80/t+40/n+20/p to M−1, the periodindicated by N is 10 ms, then the SRS is transmitted by using offsetN−320/f−160/m−80/t−40/n−20/p;

Reserved by the system if the range of N is from M to320/f+160/m+80/t+40/n+20/p+10/x−1;

If the range of N is from 320/f+160/m+80/t+40/n+20/p+10/x to M−1, theperiod indicated by N is 5 ms, then the SRS is transmitted by usingoffset N−320/f−160/m−80/t−40/n−20/p−10/x; AND

Reserved if the range of N is from M to320/f+160/m+80/t+40/n+20/p+10/x+5−1.

Where f, m, t, n can be 1, 2, 4, 8; p can be 1, 2, 4, 5, 10; x can be 1,2, 5; M presents the number of OFDM symbol configured to transmit SRS ina period in the whole cell indicated by the information N. The value off, m, t, n and M need to be set statically in system specification. “−”is a symbol for subtraction.

The design method described above is the most basic SRS design for thedesignated user. The invention considers the coherence of signal formatin LTE FDD and LTE TDD, the detailed principle is as follows: firstly,the information bits indicating the SRS transmission of designated userin LTE FDD and LTE TDD is the same. For example, 10 bits or 9 bits areused to inform. Next, the reserved index occupies and only occupies onesection of continuous indexes both in LTE FDD and LTE TDD.

According to the design principle of LTE TDD compatible with of LTE FDD,the SRS transmission signal for designated user can refer to a tablebelow:

TABLE 1 Indexes of SRS signal index period offset description 0-4 5 0-4Configuration 3, 4 and 5 are reserved in LTE TDD  5-14 10 0-9 15-34 200-19 35-74 40 0-39  75-154 80 0-79 155-314 160 0-159 315-634 320 0-319 635-1023 2 0-1 in FDD indexes 637-1023 are 0-9 for TDD reserved in LTEFDD indexes 645-1023 are reserved in LTE TDD The offset in LTE TDD isthe index of method, using which to select two SRS symbols fromhalf-frame

Follow table is used to describe by using the same design principle:

TABLE 2 Indexes of SRS signal Index Period Offset Description  0-319 3200-319 320-479 160 0-159 480-559 80 0-79 560-599 40 0-39 600-619 20 0-19620-629 10 0-9 630-634 5 0-4 Configuration 3, 4 and 5 are reserved inLTE TDD  635-1023 2 0-1 in FDD indexes 637-1023 are 0-9 for TDD reservedin LTE FDD indexes 645-1023 are reserved in LTE TDD The offset in LTETDD is the index of method, using which to select two SRS symbols fromhalf-frame

Considering the period value could be ordered from small to large, atable uniformly describing the indexes of SRS signal for LTE TDD and LTEFDD could be obtained:

TABLE 3 Indexes of SRS signal Index Period Offset Description 0-9 2 0-1:LTE 2-9 reserved in LTE FDD FDD 0-9: LTE The offset in LTE FDD TDD isthe index of method, using which to select two SRS symbols fromhalf-frame 10-14 5 0-4 Configuration 3, 4 and 5 are reserved in LTE TDD15-24 10 0-9 25-44 20 0-19 45-84 40 0-39  85-164 80 0-79 165-324 1600-159  325-1023 320 0-1 in FDD indexes 645-1023 are 0-9 for TDD reservedin LTE TDD

In order to ensure a coherence of design for LTE FDD and LTE TDD, adegree of flexibility may be sacrificed in LTE TDD. If period is 2 ms,the number of indexes is limited to 2 in LTE TDD, so that the number ofindexes in LTE FDD and LTE TDD is exactly the same. This is shown inTable 4:

TABLE 4 Indexes of SRS signal Index Period Offset Description 0-1 2 0-12-6 5 0-4 Configuration 3, 4 and 5 are reserved in LTE TDD  7-16 10 0-917-36 20 0-19 37-76 40 0-39  77-156 80 0-79 157-316 160 0-159  317-1023320 0-1 in FDD indexes 637-1023 are 0-9 for TDD reserved

In the above method, considering the coherence for LTE FDD and LTE TDD,the configuration in both systems should keep the same. The detailedmethod for LTE TDD is optimized. If using different table for LTE FDDand LTE TDD is allowed, table 1 to 4 could just used in LTE TDD, andanother design for LTE FDD is achievable. The mainly difference is thatin LTE FDD, only two indexes are occupied in 2 ms period.

The above description is the SRS configuration method based on theredefinition of 2 ms and 5 ms period in LTE TDD. For redefinition of the2 ms period of configuration 0 to 2 and 6, the actual period is 5 ms.For redefinition of the 2 ms period of configuration 3 to 5, theactually period is 10 ms. So that when using the period value of SRS forcalculation, for the 2 ms period of configuration 0 to 2 and 6, 5 ms isused as the period, and for the 2 ms period of configuration 3 to 5, 10ms is used as the period.

If the redefinition of 2 ms and 5 ms period in LTE TDD is not used, insome situation without supporting 2 ms and 5 ms period, the systemdefines that two SRS is configured in 5 ms or 10 ms. When using theperiod of SRS, the value of period is used to calculate directly. Table5 and table 6 are two possible detailed configuration methods. Theperiod value in table 5 or table 6 is an actual period value. It isassumed that all of C (5,2)=10 methods of selecting two SRS symbols inhalf-frame are supported.

In table 5, when the index is between 0 and 9, two SRS are configured ina period of 5 ms. The corresponding offset 0 to 9 is the indexes for themethods for selecting two SRS symbols from half-frame substantially.When the index is between 10 and 14, one SRS is configured in a periodof 5 ms, and the offset presents a position of assigned SRS. When theindex is between 15 and 24, two SRS are configured in a period of 10 ms.The corresponding offset 0 to 9 is the index for the methods forselecting two SRS symbols from half-frame substantially. When the indexis between 25 and 34, one SRS is configured in a period of 10 ms, andthe offset presents the position of assigned SRS.

TABLE 5 Indexes of SRS signal Index Period Offset Description 0-9 5 0-9The offset is the index of method, using which to select two SRS symbolsfrom half-frame 10-14 5 0-4 15~24 10 0~9 The offset is the index ofmethod, using which to select two SRS symbols from half-frame 25-34 100-9 35-54 20  0-19 55-94 40  0-39  95-174 80  0-79 175-334 160  0-159335-654 320  0-319  655-1023 Reserved

Table 6 has the same effect as that of Table 5 except for an order ofrows to implement a new embodiment. The invention is limited to theorder of SRS period in the table.

In table 6, when the index is between 0 and 9, two SRS are configured ina period of 5 ms. The corresponding offset 0 to 9 is the index of themethods, for selecting two SRS symbols from half-frame substantially.When the index is between 10 and 19, two SRS are configured in a periodof 10 ms. The corresponding offset 0 to 9 is the index of the methodsfor selecting two SRS symbols from half-frame substantially. When theindex is between 20 and 24, one SRS is configured in a period of 5 ms,and the offset presents the position of assigned SRS. When the index isbetween 25 and 34, one SRS is configured in a period of 10 ms, and theoffset value presents the position of assigned SRS.

TABLE 6 Indexes of SRS signal Index Period Offset Description 0-9 5 0-9The offset is the index of method, using which to select two SRS symbolsfrom half-frame 10-19 10 0-9 The offset is the index of method, usingwhich to select two SRS symbols from half-frame 20~24 5 0~4 25-34 10 0-935-54 20  0-19 55-94 40  0-39  95-174 80  0-79 175-334 160  0-159335-654 320  0-319  655-1023 Reserved

If the redefinition of 2 ms and 5 ms period in LTE TDD is not used, theperiod of 2 ms not supported in LTE TDD is defined and two SRS areconfigured every half-frame (5 ms). So that, when using the period valueof SRS for calculating, for configuration 0 to 2 and 6, 5 ms is used asthe period, for configuration 3 to 5, 10 ms is used as the period. Table6 is a possible configuration method. It is assumed that all theC(5,2)=10 methods used to select two SRS symbols in half-frame aresupported.

In table 7, when the index is between 0 and 9, two SRS are configured ina period of 5 ms. The corresponding offset 0 to 9 is the index of themethods for selecting two SRS symbols from half-frame. When the index isbetween 10 and 14, one SRS is configured in a period of 5 ms, and theoffset indicates the position of the assigned SRS. When the index isbetween 15 and 24, one SRS is configured in a period of 10 ms, and theoffset presents the position of assigned SRS.

TABLE 7 Indexes of SRS signal Index Period Offset Description 0-9 5 0-9The offset is the index of method, using which to select two SRS symbolsfrom half-frame 10-14 5 0-4 15-24 10 0-9 25-44 20  0-19 45-84 40  0-39 85-164 80  0-79 165-324 160  0-159 325-644 320  0-319  645-1023Reserved

C(5,2)=10 indexes are used to achieve complete flexibility fortransmitting two SRS in a period. A mapping method from the indexes totwo selected SRS symbol is as follows: when UpPTS includes two SRSsymbols, a first SRS symbol is indicated by SRS sub-frame offset 0 and asecond SRS symbol is indicated by SRS sub-frame offset 1. When UpPTSincludes one SRS symbol, the SRS symbol is indicated by SRS sub-frameoffset 1. The SRS symbol in the other sub-frame is indicted by thecorresponding offset (that is, 2, 3 or 4). Therefore, a possible mappingmethod from C(5,2)=10 indexes to two selected SRS symbols is shown asfollows:

TABLE 8 Mapping from 10 indexes to two selected SRS symbols Index Offset0 0, 1 1 0, 2 2 1, 2 3 0, 3 4 1, 3 5 0, 4 6 1, 4 7 2, 3 8 2, 4 9 3, 4

The network uses RRC signal to transmit the SRS signal generated in step1.

The generated SRS information is mapped to transmission channel andphysical channel, then transmitted to UE through the antenna after beingprocessed accordingly.

An apparatus for transmitting SRS of designated user is illustrated inFIG. 3. The apparatus includes a SRS generator module (301) forgenerating the SRS information. The SRS information is mapped to atransmission channel module (302), passed to a physical channel mappingmodule (303), and the SRS of designated user is transmitted through theantenna (304).

The apparatus (406) for transmitting the SRS in LTE UE is illustrated inFIG. 4. The apparatus (406) includes a module (401) which generates anSRS sequence based on the SRS information of designated user received bya module (402) and the other information (such as the cycle offset usedto transmit SRS, comb, the bandwidth and so on) received by a module(403). Under the control of a module (404), the power is adjusted by amodule (405) in the physical resource allocated at a proper timing andthe SRS of designated user is transmitted by using an antenna module(407).

Two examples according to present invention are described as follows. Inorder to avoid making the description ambiguous, detailed descriptionsfor known functions are omitted.

A First Example

Configuration 1(502) in LTE TDD is applied in this example.

The signal information indicating the SRS transmission of designateduser is generated by the LTE network. According to the table 1, theindex 635 is selected. For LTE TDD, the index means the period is 2 ms,indicating that the designated user transmits SRS in the first andsecond symbol in UpPTS (601 or 604). For LTE FDD, the index means thatthe designated user may use the available OFDM symbol in the firstsub-frame in the 2 ms frame to transmit SRS. Then, via the transmissionchannel mapping and physical channel mapping, the system transmits theindex information to the designated user.

A Second Example

Configuration 3(504) in LTE TDD is applied in this example.

The signal information indicating the SRS transmission of designateduser is generated by the LTE network. According to the table 1, theindex 637 which indicates that the period is 2 ms is selected. For LTETDD, the index means that the designated user transmits SRS in the firstsymbol (701) and the first normal uplink sub-frame (sub-frame 2) (702).For LTE FDD, the index is reserved by the system and the system doesn'tuse the index to transmit SRS information of designated user. Then,after the transmission channel mapping and physical channel mapping, thesystem transmit s the index information to the designated user.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the present invention as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method for transmitting a sounding referencesignal (SRS) by a user equipment (UE), the method comprising: receivingindex information related to the SRS; determining an SRS offset based onthe index information; transmitting the SRS based on the SRS offset,wherein, if the index information is an integer from 0 to 9, the SRSoffset indicated by the index information is based on: Index Offset 0 4,1 1 0, 2 2 1, 2 3 0, 3 4 1, 3 5 0, 4 6 1, 4 7 2, 3 8 2, 4 9  3,
 4.


2. The method of claim 1, wherein the SRS offset being 0 indicates theSRS is located to a first symbol of an uplink pilot time slot (UpPTS)and the SRS offset being 1 indicates the SRS is located to a secondsymbol of the UpPTS, if the UpPTS comprises two symbols in a specialsubframe.
 3. The method of claim 1, wherein the SRS offset being 1indicates the SRS is located to a first symbol of an uplink pilot timeslot (UpPTS), if the UpPTS comprises a symbol in a special subframe. 4.The method of claim 1, wherein the SRS offset being 2, 3, and 4indicates the SRS is located to a symbol in a second subframe, a thirdsubframe, and a fourth subframe.
 5. The method of claim 1, wherein, ifthe index information is an integer greater than 9, the SRS offset andan SRS period are determined based on the index information accordingto: Index Period Offset Description 10-14 5 0-4 15-24 10 0-9 25-44 20 0-19 45-84 40  0-39  85-164 80  0-79 165-324 160  0-159 325-644 320 0-319  645-1023 Reserved.


6. A method of receiving a sounding reference signal (SRS) by a basestation, the method comprising: transmitting index information relatedto the SRS; and receiving the SRS based on an SRS offset that is basedon the index information, wherein, if the index information is aninteger from 0 to 9, the SRS offset indicated by the index informationis based on: Index Offset 0 0, 1 1 0, 2 2 1, 2 3 0, 3 4 1, 3 5 0, 4 6 1,4 7 2, 3 8 2, 4 9  3,
 4.


7. The method of claim 6, wherein the SRS offset being 0 indicates theSRS is located to a first symbol of an uplink pilot time slot (UpPTS)and the SRS offset being 1 indicates the SRS is located to a secondsymbol of the UpPTS, if the UpPTS comprises two symbols in a specialsubframe.
 8. The method of claim 6, wherein the SRS offset being 1indicates the SRS is located to a first symbol of an uplink pilot timeslot (UpPTS), if the UpPTS comprises a symbol in a special subframe. 9.The method of claim 6, wherein the SRS offset being 2, 3, and 4indicates the SRS is located to a symbol in a second subframe, a thirdsubframe, and a fourth subframe.
 10. The method of claim 6, wherein, ifthe index information is an integer greater than 9, the SRS offset andan SRS period are determined based on the index information accordingto: Index Period Offset Description 10-14 5 0-4 15-24 10 0-9 25-44 20 0-19 45-84 40  0-39  85-164 80  0-79 165-324 160  0-159 325-644 320 0-319  645-1023 Reserved.


11. A user equipment (UE) apparatus for transmitting a soundingreference signal (SRS), the UE apparatus comprising: a transceiver fortransmitting and receiving signals to and from a base station; and acontroller for receiving index information related to the SRS, fordetermining an SRS offset based on the index information, and fortransmitting the SRS based on the SRS offset, wherein, if the indexinformation is an integer from 0 to 9, the SRS offset indicated by theindex information is based on: Index Offset 0 0, 1 1 0, 2 2 1, 2 3 0, 34 1, 3 5 0, 4 6 1, 4 7 2, 3 8 2, 4 9  3,
 4.


12. The UE apparatus of claim 11, wherein the SRS offset being 0indicates the SRS is located to a first symbol of an uplink pilot timeslot (UpPTS) and the SRS offset being 1 indicates the SRS is located toa second symbol of the UpPTS, if the UpPTS comprises two symbols in aspecial subframe.
 13. The UE apparatus of claim 11, wherein the SRSoffset being 1 indicates the SRS is located to a first symbol of anuplink pilot time slot (UpPTS), if the UpPTS comprises a symbol in aspecial subframe.
 14. The UE apparatus of claim 11, wherein the SRSoffset being 2, 3, and 4 indicates the SRS is located to a symbol in asecond subframe, a third subframe, and a fourth subframe.
 15. The UEapparatus of claim 11, wherein, if the index information is an integergreater than 9, the SRS offset and an SRS period are determined based onthe index information according to: Index Period Offset Description10-14 5 0-4 15-24 10 0-9 25-44 20  0-19 45-84 40  0-39  85-164 80  0-79165-324 160  0-159 325-644 320  0-319  645-1023 Reserved.


16. A base station for receiving a sounding reference signal (SRS), thebase station comprising: a transceiver for transmitting and receivingsignals to and from a user equipment (UE); and a controller fortransmitting index information related to the SRS, and for receiving theSRS based on an SRS offset that is based on the index information,wherein, if the index information is an integer from 0 to 9, the SRSoffset indicated by the index information is based on: Index Offset 0 0,1 1 0, 2 2 1, 2 3 0, 3 4 1, 3 5 0, 4 6 1, 4 7 2, 3 8 2, 4 9  3,
 4.


17. The base station of claim 16, wherein the SRS offset being 0indicates the SRS is located to a first symbol of an uplink pilot timeslot (UpPTS) and the SRS offset being 1 indicates the SRS is located toa second symbol of the UpPTS, if the UpPTS comprises two symbols in aspecial subframe.
 18. The base station of claim 16, wherein the SRSoffset being 1 indicates the SRS is located to a first symbol of anuplink pilot time slot (UpPTS), if the UpPTS comprises a symbol in aspecial subframe.
 19. The base station of claim 16, wherein the SRSoffset being 2, 3, and 4 indicates the SRS is located to a symbol in asecond subframe, a third subframe, and a fourth subframe.
 20. The basestation of claim 16, wherein, if the index information is an integergreater than 9, the SRS offset and an SRS period are determined based onthe index information according to: Index Period Offset Description10-14 5 0-4 15-24 10 0-9 25-44 20  0-19 45-84 40  0-39  85-164 80  0-79165-324 160  0-159 325-644 320  0-319  645-1023 Reserved.